Known metering pump aggregates have a metering chamber, which is bordered on one side by a positive-displacement body, for example in the form of a membrane. The positive-displacement body can change the metering chamber, thereby achieving a pumping effect. A suitable linear drive is provided for driving the positive-displacement body. For example, this can be a rotationally driving drive motor in form of a stepping motor, which imparts a linearly oscillating motion to a connecting rod by way of a cam. Arranged on the input and output side of the metering chamber are check valves, which during an intake stroke prevent the medium to be conveyed from flowing out of the pressure line back into the metering chamber, and during the pressure stroke prevent the medium from being forced into the intake line instead of the pressure line.
When metering very low volumes or conveyed flows, for example a few milliliters per hour, very slow stroke rates are required; for example a pressure stroke can require several minutes, even longer than fifteen minutes. At these very slow stroke and conveying rates, the lack of dynamics makes it impossible to ensure that the valves will close faster, which leads to leaks, and hence poor metering accuracy.